Process for the production of copolycarbonates with reduced color

ABSTRACT

A method is provided for reducing the color generated during production of copolycarbonate that includes quinone-type residues. The method includes the steps preparing a reaction mixture containing precursors of monomer residues, selecting a catalyst introduction strategy and adding catalysts according to the strategy. The strategy is sufficient to result in a product copolycarbonate with improved color. The method further includes the steps of introducing the reaction mixture to a series of process units and allowing the reaction mixture to polymerize thereby forming a copolycarbonate. The resulting copolycarbonate has improved color as compared to a copolycarbonate formed in a process without the steps of selecting a catalyst introduction strategy and introducing catalysts according to the selected strategy.

BACKGROUND OF THE INVENTION

Polycarbonate is a thermoplastic that has excellent mechanicalproperties such as impact resistance, heat resistance and transparency.Polycarbonates are widely used in applications ranging from footballhelmets to automobile parts to transparent security windows. Morerecently, polycarbonates have also proven to be the material of choicefor optical media applications such as optical discs, for examplecompact discs (CD) and digital versatile discs (DVD). Conventionalpolycarbonates are usually produced by (1) an interfacialpolymerization, in which bisphenol A (BPA) is reacted directly withphosgene or (2) a melt polymerization process in which BPA istransesterified with a carbonic acid diester such as diphenyl carbonate(DPC). For many applications, there has been a need for materialspossessing the fundamental characteristics of transparency and toughnessinherent in BPA polycarbonate but possessing, in addition, certainimprovements in physical properties relative those possessed bybisphenol A polycarbonate (BPA-PC), for example reduced birefringencefor optical applications. For some applications improved chemicalresistance relative to BPA polycarbonate is required, for example incertain medical and automotive applications. Copolycarbonates arematerials frequently possessing the fundamental traits of BPApolycarbonate, transparency and toughness, but in certain instances alsopossessing improved performance characteristics for a given applicationrelative to BPA polycarbonate.

One example of such a copolycarbonate comprises repeat units derivedfrom resorcinol or hydroquinone in addition to repeat units derived frombisphenol A. The incorporation of resorcinol-derived andhydroquinone-derived repeat units into a BPA-polycarbonate confersexcellent melt flow properties, molding properties, solvent and heatresistance, while maintaining the excellent mechanical properties andtransparency inherent in bisphenol A polycarbonate. Suchcopolycarbonates can be prepared by interfacial polymerization, meltpolymerization, or solid state polymerization. (U.S. Pat. No.6,177,536). The present invention relates to an improved method toprepare these and related copolycarbonates using the melt polymerizationmethod.

SUMMARY OF THE INVENTION

Applicants have determined that the formation of color in quinone-likecopolycarbonates is affected by the point of addition of polymerizationcatalysts to the melt polymerization process. Thus, an embodiment of thepresent invention provides a method of producing a copolycarbonate withimproved color wherein the method comprises the steps of,

-   i. preparing a molten reaction mixture comprising a first dihydroxy    aromatic compound comprising monomer residue (a), a second dihydroxy    aromatic compound comprising monomer residue (b), and a carbonate    source,    -   wherein monomer residue (a) is a quinone structure, or a        structure capable of forming a quinone structure upon oxidation,    -   wherein monomer residue (b) is a quinone structure, or a        structure capable of forming a quinone structure upon oxidation        different from monomer residue (a) or is,

-   -    where B is

-   -    —O—, —CO—, —S—, —SO₂—, a C₆–C₂₀ aromatic radical, or a C₆–C₂₀        cycloaliphatic radical; the groups R¹ and R² are independently a        hydrogen atom, C₁–C₂₀ alkyl radical, C₄–C₂₀ cycloalkyl radical,        or C₄–C₂₀ aryl radical; or R¹ and R² together form a C₄–C₂₀        cycloaliphatic ring which is optionally substituted by one or        more C₁–C₂₀ alkyl, C₆–C₂₀ aryl, C₅–C₂₁ aralkyl, C₅–C₂₀        cycloalkyl groups or a combination thereof, R³ is a divalent        hydrocarbylene group, and R⁴ and R⁵ are independently a hydrogen        atom, halogen atom, nitro group, cyano group, C₁–C₂₀ alkyl        radical C₄–C₂₀ cycloalkyl radical, or C₆–C₂₀ aryl radical and p        and q are both integers from 0 to 4,

-   ii. selecting a catalyst introduction strategy sufficient to result    in a product copolycarbonate with improved color, wherein the    catalyst introduction strategy is selected from the group consisting    of,    -   1. introducing a polymerization catalyst to the molten reaction        mixture after monomer residues (a), monomer residues (b), and        carbonate source are melted and prior to substantial        polymerization,    -   2. introducing a polymerization catalyst to the reaction mixture        or monomer residues prior to melting with the proviso that        residence time of the process from the start of melting until        substantial polymerization has occurred is less than 4 hours,        and    -   3. or a combination thereof,    -   wherein the polymerization catalyst is an inorganic catalyst, an        organic catalyst, or both inorganic and organic catalyst which        may be introduced separately or together,

-   iii. introducing the catalyst according to the selected catalyst    introduction strategy,

-   iv. introducing the reaction mixture to a series of process units,    and

-   v. allowing the reaction mixture to polymerize in the series of    process units thereby forming copolycarbonate, wherein the    copolycarbonate has improved color as compared to a copolycarbonate    formed in a melt process without the steps of selecting a catalyst    introduction strategy and introducing catalyst according to the    selected strategy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of an embodiment of a melt polymerization processof the current invention.

FIG. 2 is a bar graph that charts the comparative examples and inventionexamples from the examples section of the present application.

DETAILED DESCRIPTION OF THE INVENTION

The present invention may be understood more readily by reference to thefollowing detailed description of preferred embodiments of the inventionand the examples included therein. The present invention provides amethod for improving the color of a copolycarbonate produced by meltpolymerization wherein the copolycarbonate comprises monomer residues ofdihydroxy aromatic compounds and carbonates. The method comprises thesteps of; preparing a reaction mixture comprising precursors of themonomer residues; selecting a catalyst introduction strategy sufficientto result in a product copolycarbonate with improved color; introducinga catalyst to the reaction mixture according to the selected catalystintroduction strategy; introducing the reaction mixture to a series ofprocess units; and allowing the reaction mixture to polymerize therebyforming copolycarbonate, wherein the copolycarbonate has improved coloras compared to a copolycarbonate formed in a melt process without thesteps of selecting a catalyst introduction strategy and introducingcatalyst according to the selected strategy.

In the specification and the claims which follow, reference will be madeto a number of terms which shall be defined to have the followingmeanings:

The singular forms “a”, “an” and “the” include plural referents unlessthe context clearly dictates otherwise.

“Optional” or “optionally” means that the subsequently described eventor circumstance may or may not occur, and that the description includesinstances where the event occurs and instances where it does not.

“Copolycarbonate” refers to polycarbonates incorporating repeat unitsderived from at least two dihydroxy aromatic compounds and includescopolyestercarbonates, for example a polycarbonate comprising repeatunits derived from resorcinol, bisphenol A, and dodecandioic acid.Nothing in the description and claims of this application should betaken as limiting the copolycarbonate to only two dihydroxy aromaticresidues unless the context is expressly limiting. Thus, the applicationencompasses copolycarbonates with residues of 2, 3, 4, or more types ofdihydroxy aromatics.

“BPA” is herein defined as bisphenol A or2,2-bis(4-hydroxyphenyl)propane.

“Substantial polymerization” is where the average molecular weight(M_(w)) of the copolycarbonate is less than 5,000 (PS standards).

“Melt polycarbonate” refers to a polycarbonate made by thetransesterification of a diarylcarbonate with a dihydroxy aromaticcompound.

“Catalyst system” as used herein refers to a catalyst or catalysts thatcatalyze the transesterification of a dihydroxy aromatic compound with adiarylcarbonate in the preparation of melt polycarbonate.

“Catalytically effective amount” refers to an amount of a catalyst atwhich catalytic performance is exhibited.

“Catalyst introduction strategy” refers to the method of adding thecatalysts to the reaction mixture. The catalyst introduction strategymay include the introduction of catalysts to the reaction mixture as itis prepared or as the reaction mixture passes through a series ofprocess equipment.

“Monomer mix tank” refers to the area of the process wherein thereaction mixture is prepared. The word tank does not limit the inventionto the mixing of monomers within a single vessel. The mixing may occurin a series of tanks or by any other means to prepare a mixture.

“Process units” refers to the area within the system wherein themonomers react and where copolycarbonate weight is built. This may occurwithin, among other places, extruders, equilibration vessels,continuously stirred tank reactors, batch reactors, packed bed reactorsor heat exchangers.

“Plaque Yellowness Index” refers to a measurement of color of a sampleof copolycarbonate using a UV spectrophotometer converted to a 1 mmthick sample value. It is preferable that the copolycarbonate made bythe method of the present invention have a plaque yellowness index valueof between 0.4 and 8.0, more preferably between 0.04 and 5.0 and stillmore preferably between 0.04 and 3.0. The plaque YI of the resultingcopolycarbonate is affected by the initial quality of the quinone typestructure.

“Solution Yellowness Index” refers to the yellowness of the reactionmixture prior to substantial polymerization. Data can be measured with aUV/VIS spectrophotometer on a 10% Copolymer solution in MECl₂. Thetransmission can be measured on 3 wavelengths (445 nm, 555 nm, and 600nm) against a MeCl₂ blank. With the following calculation the sol YI canbe calculated; (Sol YI=(% T600−% T445)/% T555*100%).

“Dihydroxy aromatic compound(s)” means an aromatic compound whichcomprises two hydroxy groups on one or more aromatic rings, for examplea bisphenol such as bisphenol A or a dihydroxy benzene such asresorcinol.

“Aromatic radical” refers to a radical having a valence of at least onecomprising at least one aromatic group. Examples of aromatic radicalsinclude phenyl, pyridyl, furanyl, thienyl, naphthyl, phenylene, andbiphenyl. The term includes groups containing both aromatic andaliphatic components, for example a benzyl group.

“Cycloaliphatic radical” refers to a radical having a valance of atleast one comprising an array of atoms which is cyclic but which is notaromatic. The array may include heteroatoms such as nitrogen, sulfur andoxygen or may be composed exclusively of carbon and hydrogen. Examplesof cycloaliphatic radicals include cyclopropyl, cyclopentyl cyclohexyl,tetrahydrofuranyl and the like.

Numerical values in the specification and claims of this application,particularly as they relate to polymer compositions, reflect averagevalues for a composition that may contain individual polymers ofdifferent characteristics. Furthermore, the numerical values should beunderstood to include numerical values which are the same when reducedto the same number of significant figures and numerical values whichdiffer from the stated value by less than the experimental error of themeasurement technique used in the present application to determine thevalue.

The present invention provides a method for preparing a copolycarbonate.An embodiment of the method comprises contacting under meltpolymerization conditions a first dihydroxy aromatic compound containingthe precursor of monomer residue (a), and a second dihydroxy aromaticcompound containing the precursor of monomer residue (b), with at leastone carbonate source, and at least one melt polymerization catalyst.

The First Dihydroxy Aromatic Compound:

The first dihydroxy aromatic compound comprises monomer residue (a). Itcan be any quinone structure or structure capable of forming a quinonestructure upon oxidation. Suitable types of these dihydroxy aromaticcompounds may be selected from the group consisting of dihydroxybenzenes having structure III

where each R¹⁰ is independently at each occurrence a hydrogen atom,halogen atom, nitro group, cyano group, C₁–C₂₀ alkyl, C₄–C₂₀ cycloalkylradical, C₄–C₂₀ aryl radical, and n is an integer from 0 to 4.

Non-limiting examples of dihydroxy benzenes having structure III areresorcinol; hydroquinone; 4-methylresorcinol; 5-methylresorcinol;2-methylhydroquinone; 2-ethylhydroquinone; 2,5-dimethylhydroquinone;2,6-dimethylhydroquinone; catechol; 3-methylcatechol; 4-methylcatechol;butylhydroquinone; and mixtures thereof.

The Second Dihydroxy Aromatic Compound:

The second dihydroxy aromatic compound forms the precursor of monomerresidue (b) such that the polymer formed is a copolycarbonate. It can beany quinone structure or structure capable of forming a quinonestructure upon oxidation different from monomer residue (a). Suitabletypes of these dihydroxy aromatic compounds again may be selected fromthe group consisting of dihydroxy benzenes having structure III

where each R¹⁰ is independently at each occurrence a hydrogen atom,halogen atom, nitro group, cyano group, C₁–C₂₀ alkyl, C₄–C₂₀ cycloalkylradical, C₄–C₂₀ aryl radical, and n is an integer from 0 to 4.

Non-limiting examples of dihydroxy benzenes having structure III areresorcinol; hydroquinone; 4-methylresorcinol; 5-methylresorcinol;2-methylhydroquinone; 2-ethylhydroquinone; 2,5-dimethylhydroquinone;2,6-dimethylhydroquinone; catechol; 3-methylcatechol; 4-methylcatechol;butylhydroquinone; and mixtures thereof.

Alternatively the second dihydroxy aromatic compound may be a bisphenolhaving structure IV

where B is,

—O—, —CO—, —S—, —SO₂—, a C₆–C₂₀ aromatic radical, or a C₆–C₂₀cycloaliphatic radical; the groups R¹ and R² are independently ahydrogen atom, C₁–C₂₀ alkyl radical, C₄–C₂₀ cycloalkyl radical, orC₄–C₂₀ aryl radical; or R¹ and R² together form a C₄–C₂₀ cycloaliphaticring which is optionally substituted by one or more C₁–C₂₀ alkyl, C₆–C₂₀aryl, C₅–C₂₁, aralkyl, C₅–C₂₀ cycloalkyl groups or a combinationthereof, R³ is a divalent hydrocarbylene group, and R⁴ and R⁵ areindependently a hydrogen atom, halogen atom, nitro group, cyano group,C₁–C₂₀ alkyl radical C₄–C₂₀ cycloalkyl radical, or C₆–C₂₀ aryl radicaland p and q are both integers from 0 to 4.

Bisphenols having structure IV are illustrated by2,2-bis(4-hydroxyphenyl)propane (bisphenol A);2,2-bis(3-chloro-4-hydroxyphenyl)propane;2,2-bis(3-bromo-4-hydroxyphenyl)propane;2,2-bis(4-hydroxy-3-methylphenyl)propane;2,2-bis(4-hydroxy-3-isopropylphenyl)propane;2,2-bis(3-t-butyl-4-hydroxyphenyl)propane;2,2-bis(3-phenyl-4-hydroxyphenyl)propane;2,2-bis(3,5-dichloro-4-hydroxyphenyl)propane;2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane;2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane;2,2-bis(3chloro-4-hydroxy-5-methylphenyl)propane;2,2-bis(3-bromo-4-hydroxy-5-methylphenyl)propane;2,2-bis(3-chloro-4-hydroxy-5-isopropylphenyl)propane;2,2-bis(3-bromo-4-hydroxy-5-isopropylphenyl)propane;2,2-bis(3-t-butyl-5-chloro-4-hydroxyphenyl)propane;2,2-bis(3-bromo-5-t-butyl-4-hydroxyphenyl)propane;2,2-bis(3-chloro-5-phenyl-4-hydroxyphenyl)propane;2,2-bis(3-bromo-5-phenyl-4-hydroxyphenyl)propane;2,2-bis(3,5-disopropyl-4-hydroxyphenyl)propane;2,2-bis(3,5-di-t-butyl-4-hydroxyphenyl)propane;2,2-bis(3,5-diphenyl-4-hydroxyphenyl)propane;2,2-bis(4-hydroxy-2,3,5,6-tetrachlorophenyl)propane;2,2-bis(4-hydroxy-2,3,5,6-tetrabromophenyl)propane;2,2-bis(4-hydroxy-2,3,5,6-tetramethylphenyl)propane;2,2-bis(2,6-dichloro-3,5-dimethyl-4-hydroxyphenyl)propane;2,2-bis(2,6-dibromo-3,5-dimethyl-4-hydroxyphenyl)propane;1,1-bis(4-hydroxyphenyl)cyclohexane;1,1-bis(3-chloro-4-hydroxyphenyl)cyclohexane;1,1-bis(3-bromo-4-hydroxyphenyl)cyclohexane;1,1-bis(4-hydroxy-3-methylphenyl)cyclohexane;1,1-bis(4-hydroxy-3-isopropylphenyl)cyclohexane;1,1-bis(3-t-butyl-4-hydroxyphenyl)cyclohexane;1,1-bis(3-phenyl-4-hydroxyphenyl)cyclohexane;1,1-bis(3,5-dichloro-4-hydroxyphenyl)cyclohexane;1,1-bis(3,5-dibromo-4-hydroxyphenyl)cyclohexane;1,1-bis(3,5-dimethyl-4-hydroxyphenyl)cyclohexane;1,1-bis(3-chloro-4-hydroxy-5-methylphenyl)cyclohexane;1,1-bis(3-bromo-4-hydroxy-5-methylphenyl)cyclohexane;1,1-bis(3-chloro-4-hydroxy-5-isopropylphenyl)cyclohexane;1,1-bis(3-bromo-4-hydroxy-5-isopropylphenyl)cyclohexane;1,1-bis(3-t-butyl-5-chloro-4-hydroxyphenyl)cyclohexane;1,1-bis(3-bromo-5-t-butyl-4-hydroxyphenyl)cyclohexane;1,1-bis(3-chloro-5-phenyl-4-hydroxyphenyl)cyclohexane;1,1-bis(3-bromo-5-phenyl-4-hydroxyphenyl)cyclohexane;1,1-bis(3,5-disopropyl-4-hydroxyphenyl)cyclohexane;1,1-bis(3,5-di-t-butyl-4-hydroxyphenyl)cyclohexane;1,1-bis(3,5-diphenyl-4-hydroxyphenyl)cyclohexane;1,1-bis(4-hydroxy-2,3,5,6-tetrachlorophenyl)cyclohexane;1,1-bis(4-hydroxy-2,3,5,6-tetrabromophenyl)cyclohexane;1,1-bis(4-hydroxy-2,3,5,6-tetramethylphenyl)cyclohexane;1,1-bis(2,6-dichloro-3,5-dimethyl-4-hydroxyphenyl)cyclohexane;1,1-bis(2,6-dibromo-3,5-dimethyl-4-hydroxyphenyl)cyclohexane;1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-chloro-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-bromo-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(4-hydroxy-3-methylphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(4-hydroxy-3-isopropylphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-t-butyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-phenyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3,5-dichloro-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3,5-dibromo-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3,5-dimethyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-chloro-4-hydroxy-5-methylphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-bromo-4-hydroxy-5-methylphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-chloro-4-hydroxy-5-isopropylphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-bromo-4-hydroxy-5-isopropylphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-t-butyl-5-chloro-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-bromo-5-t-butyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;bis(3-chloro-5-phenyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-bromo-5-phenyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3,5-disopropyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3,5-di-t-butyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3,5-diphenyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(4-hydroxy-2,3,5,6-tetrachlorophenyl)-3,3,5-trimethylcyclohexane;1,1-bis(4-hydroxy-2,3,5,6-tetrabromophenyl)-3,3,5-trimethylcyclohexane;1,1-bis(4-hydroxy-2,3,5,6-tetramethylphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(2,6-dichloro-3,5-dimethyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(2,6-dibromo-3,5-dimethyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;4,4′dihydroxy-1,1-biphenyl; 4,4′-dihydroxy-3,3′-dimethyl-1,1-biphenyl;4,4′-dihydroxy-3,3′-dioctyl-1,1-biphenyl; 4,4′-dihydroxydiphenylether;4,4′-dihydroxydiphenylthioether;1,3-bis(2-(4-hydroxyphenyl)-2-propyl)benzene;1,3-bis(2-(4-hydroxy-3-methylphenyl)-2-propyl)benzene;1,4-bis(2-(4-hydroxyphenyl)-2-propyl)benzene; and1,4-bis(2-(4-hydroxy-3-methylphenyl)-2-propyl)benzene. In manyapplications due to its relatively high reactivity, thermal stability,and low cost, bisphenol A (BPA) is frequently preferred.

The Carbonate Source:

In the production of copolymerized polycarbonates in accordance with thepresent invention, the compounds which react with the dihydroxycompounds to form carbonate linkages (the carbonate source) may becarbonate diesters, carbonyl halides, etc. Specific examples include:diphenyl carbonate, ditolyl carbonate, bis(chlorophenyl) carbonate,m-cresyl carbonate dinaphthyl carbonate, bis(diphenyl)carbonate, diethylcarbonate, dimethyl carbonate, dibutyl carbonate, dicyclohexylcarbonate, and other carbonate diesters, phosgene, and other carbonylhalides. Of the various compounds of this type, diphenyl carbonate isoften preferred.

The carbonate can be also be derived from an activated dicarbonate or amixture of an activated carbonate with diphenyl carbonate. A preferredactivated carbonate of the present invention is an activateddiarylcarbonate such as bismethylsalicylcarbonate (BMSC). However, asused herein the term “activated carbonate” is defined as adiarylcarbonate which is more reactive than diphenylcarbonate towardtransesterification reactions. Such activated carbonates are of thegeneral formula:

wherein Ar is a substituted aromatic radical having 6 to 30 carbonatoms. The preferred activated carbonates have the more specific generalformula:

wherein Q and Q′ are each independently activating groups. A and A′ areeach independently aromatic rings which can be the same or differentdepending on the number and location of their substituent groups, and nor n′ are whole numbers of zero up to a maximum equivalent to the numberof replaceable hydrogen groups substituted on the aromatic rings A andA′, wherein a+a′ is greater than or equal to 1. R and R′ are eachindependently substituent groups such as alkyl, substituted alkyl,cycloalkyl, alkoxy, aryl, alkylaryl, cyano, nitro, halogen, andcarboalkoxy. The number of R groups is a whole number and can be 0 up toa maximum equivalent to the number of replaceable hydrogen groups on thearomatic rings A minus the number n. The number of R′ groups is a wholenumber and can be 0 up to a maximum equivalent to the number ofreplaceable hydrogen groups on the aromatic rings A minus the number n′.The number, type, and location of the R and R′ substituents on thearomatic ring are not limited unless they deactivate the carbonate andlead to a carbonate which is less reactive than diphenylcarbonate.

Non-limiting examples of activating groups Q and Q′ are: alkoxycarbonylgroups, halogens, nitro groups, amide groups, sulfone groups, sulfoxidegroups, or imine groups with structures indicated below:

Specific and non-limiting examples of activated carbonates includebis(o-methoxycarbonylphenyl)carbonate, bis(o-chlorophenyl)carbonate,bis(o-nitrophenyl)carbonate, bis(o-acetylphenyl)carbonate,bis(o-phenylketonephenyl)carbonate, bis(o-formylphenyl)carbonate.Unsymmetrical combinations of these structures, where the substitutionnumber and type on A and A′ are different, are also possible to employin the current invention. A preferred structure for an activatedcarbonate is an ester-substituted diarylcarbonate having the structure:

wherein R¹ is independently at each occurrence a C₁–C₂₀ alkyl radical,C₄–C₂₀ cycloalkyl radical, or C₄–C₂₀ aromatic radical; R² isindependently at each occurrence a halogen atom, cyano group, nitrogroup, C₁–C₂₀ alkyl radical, C₄–C₂₀ cycloalkyl radical, C₄–C₂₀ aromaticradical, C₁–C₂₀ alkoxy radical, C₄–C₂₀ cycloalkoxy radical, C₄–C₂₀aryloxy radical, C₁–C₂₀ alkylthio radical, C₄–C₂₀ cycloalkylthioradical, C₄–C₂₀ arylthio radical, C₁–C₂₀ alkylsulfinyl radical, C₄–C₂₀cycloalkylsulfinyl radical, C₄–C₂₀ arylsulfinyl radical, C₁–C₂₀alkylsulfonyl radical, C₄–C₂₀ cycloalkylsulfonyl radical, C₄–C₂₀arylsulfonyl radical, C₁–C₂₀ alkoxycarbonyl radical, C₄–C₂₀cycloalkoxycarbonyl radical, C₄–C₂₀ aryloxycarbonyl radical, C₂–C₆₀alkylamino radical, C₆–C₆₀ cycloalkylamino radical, C₅–C₆₀ arylaminoradical, C₁–C₄₀ alkylaminocarbonyl radical, C₄–C₄₀cycloalkylaminocarbonyl radical, C₄–C₄₀ arylaminocarbonyl radical, orC₁–C₂₀ acylamino radical; and b is independently at each occurrence aninteger 0–4. At least one of the substituents CO₂R¹ is preferablyattached in an ortho position relative to the carbonate group.

Examples of preferred ester-substituted diarylcarbonates include but arenot limited to bis(methylsalicyl)carbonate (CAS Registry No.82091-12-1), bis(ethyl salicyl)carbonate, bis(propyl salicyl) carbonate,bis(butylsalicyl) carbonate, bis(benzyl salicyl)carbonate, bis(methyl4-chlorosalicyl)carbonate and the like. Typicallybis(methylsalicyl)carbonate is preferred for use in melt polycarbonatesynthesis due to its lower molecular weight and higher vapor pressure.

Some non-limiting examples of non-activating groups which, when presentin an ortho position relative to the carbonate group, would not beexpected to result in activated carbonates are alkyl, cycolalkyl orcyano groups. Some specific and non-limiting examples of non-activatedcarbonates are bis(o-methylphenyl)carbonate,bis(p-cumylphenyl)carbonate,bis(p-(1,1,3,3-tetramethyl)butylphenyl)carbonate andbis(o-cyanophenyl)carbonate. Unsymmetrical combinations of thesestructures are also expected to result in non-activated carbonates.

Unsymmetrical diarylcarbonates wherein one aryl group is activated andone aryl is unactivated or de-activated would also be useful in thisinvention if the activating group renders the diaryl carbonate stillmore reactive than diphenyl carbonate.

The carbonate may also be derived from dicarboxylic acids, dicarboxylicacid esters, or dicarboxylic acid halides. Such constituent repeatingunits are typically polyester-polycarbonate units. Non-limitingexamples,of dicarboxylic acids include terephthalic acid, isophthalicacid, sebacic acid, decanedioic acid, dodecanedioic acid, etc.Non-limiting examples of dicarboxylic acid esters include diphenylsebacate, diphenyl terephthalate, diphenyl isophthalate, diphenyldecanedioate, diphenyl dodecanedioate, etc. Non-limiting examples ofdicarboxylic acid halides include terephthaloyl chloride, isophthaloylchloride, sebacoyl chloride, decanedioyl chloride, dodecanedioylchloride, etc. Such polyester-polycarbonate units may be present inproportions of up to 50 mole %, preferably not more than 30 mole %, incopolymerized polycarbonates in accordance with the present invention.

The Catalyst:

The method of the invention also comprises the step of introducing acatalyst to the reaction mixture to initiate a polymerization reaction.The catalyst may be introduced continuously, or may be introducedbatchwise and may occur before, during or after the introduction of theprecursors of monomer residues (a) or (b), or the carbonate.

The catalyst used in the method of the present invention is a base, andpreferably comprises at least one source of alkaline earth ions oralkali metal ions, and/or at least one quaternary ammonium compound, aquaternary phosphonium compound or a mixture thereof. The source ofalkaline earth ions or alkali metal ions being used in an amount suchthat the amount of alkaline earth or alkali metal ions present in thereaction mixture is in a range between about 10⁻⁵ and about 10⁻⁸ molesalkaline earth or alkali metal ion per mole of dihydroxy aromaticcompound employed.

The quaternary ammonium compound is selected from the group of organicammonium compounds having structure VI,

wherein R²⁰–R²³ are independently a C₁C₂₀ alkyl radical, C₄–C₂₀cycloalkyl radical, or a C₄–C₂₀ aryl radical; and X⁻ is an organic orinorganic anion. In one embodiment of the present invention anion X⁻ isselected from the group consisting of hydroxide, halide, carboxylate,sulfonate, sulfate, formate, carbonate, and bicarbonate.

Non-limiting examples of suitable organic ammonium compounds comprisingstructure VI are tetramethyl ammonium hydroxide, tetrabutyl ammoniumhydroxide, tetramethyl ammonium acetate, tetramethyl ammonium formateand tetrabutyl ammonium acetate. Tetramethyl ammonium hydroxide is oftenpreferred.

The quaternary phosphonium compound is selected from the group oforganic phosphonium compounds having structure VII,

wherein R²⁴–R²⁷ are independently a C¹–C²⁰ alkyl radical, C⁴–C²⁰cycloalkyl radical, or a C₄–C₂₀ aryl radical; and X⁻ is an organic orinorganic anion. In one embodiment of the present invention anion X⁻ isan anion selected from the group consisting of hydroxide, halide,carboxylate, sulfonate, sulfate, formate, carbonate, and bicarbonate.Suitable organic phosphonium compounds comprising structure VII areillustrated by tetramethyl phosphonium hydroxide, tetramethylphosphonium acetate, tetramethyl phosphonium formate, tetrabutylphosphonium hydroxide, and tetrabutyl phosphonium acetate (TBPA). TBPAis often preferred.

Where X⁻ is a polyvalent anion such as carbonate or sulfate it isunderstood that the positive and negative charges in structures VI andVII are properly balanced. For example, where R²⁰–R²³ in structure VIare each methyl groups and X⁻ is carbonate, it is understood that X⁻represents ½(CO₃ ⁻²).

Suitable sources of alkaline earth ions include alkaline earthhydroxides such as magnesium hydroxide and calcium hydroxide. Suitablesources of alkali metal ions include the alkali metal hydroxidesillustrated by lithium hydroxide, sodium hydroxide and potassiumhydroxide. Other sources of alkaline earth and alkali metal ions includesalts of carboxylic acids, such as sodium acetate and derivatives ofethylene diamine tetraacetic acid (EDTA) such as EDTA tetrasodium salt,and EDTA magnesium disodium salt. Sodium hydroxide is often preferred.

In order to achieve the formation of copolycarbonate using the method ofthe present invention an effective amount of catalyst must be employed.The amount of catalyst employed is typically based upon the total numberof moles of first dihydroxy aromatic compound and second dihydroxyaromatic compound employed in the polymerization reaction. Whenreferring to the ratio of catalyst, for example phosphonium salt VII, toall dihydroxy aromatic compounds employed in the polymerizationreaction, it is convenient to refer to moles of phosphonium salt permole of the first and second dihydroxy aromatic compounds combined,meaning the number of moles of phosphonium salt divided by the sum ofthe moles of each individual dihydroxy aromatic compound present in thereaction mixture. The amount of organic ammonium or phosphonium salts VIor VII employed typically will be in a range between about 1×10⁻² andabout 1×10⁻⁵, preferably between about 1×10⁻³ and about 1×10⁻⁴ moles permole of the first and second dihydroxy aromatic compounds combined. Theinorganic metal hydroxide catalyst typically will be used in an amountcorresponding to between about 1×10⁻⁴ and about 1×10⁻⁸, preferably1×10⁻⁴ and about 1×10⁻⁷ moles of metal hydroxide per mole of the firstand second dihydroxy aromatic compounds combined.

The Melt Process:

The term “contacting under melt polymerization conditions” will beunderstood to mean those conditions necessary to effect reaction betweenthe diarylcarbonate and the dihydroxy aromatic compounds employedaccording to the method of the present invention. The reactiontemperature is typically in the range between 150° C. and 350° C., morepreferably between 180° C. and 310° C. The pressure may be atatmospheric pressure, supra atmospheric pressure, or a range ofpressures, for example from 2 atmospheres to 15 torr in the initialstages of the polymerization reaction, and at a reduced pressure atlater stages, for example in a range between 15 torr and 0.1 torr. Thereaction time is generally in a range between 0.1 hours and 10 hours,preferably between 0.1 and 5 hours.

FIG. 1 illustrates a melt process according to an embodiment of thepresent invention. The first stage of the process is to mix the firstand second dihydroxy aromatic compounds, comprising the precursors ofmonomer residues (a) and (b), with the carbonate compound, therebyforming a reaction mixture. A catalyst is introduced to the reactionmixture according to the selected catalyst introduction strategy. Thereaction mixture is fed to a series of process equipment wherein acopolymerization reaction takes place and molecular weight of theresulting copolycarbonate is increased.

In one embodiment of the present invention, at least one first dihydroxyaromatic compound comprising the precursor of monomer residue (a) and atleast one second dihydroxy aromatic compound comprising the precursor ofmonomer residue (b) are employed in amounts such that the molar ratio ofthe first dihydroxy aromatic compound to the second dihydroxy aromaticcompound is in a range between 0.01 and 99. Where the second dihydroxyaromatic compound comprises two or more compounds, for example a mixtureof resorcinol and hydroquinone, and the first dihydroxy compound is asingle compound, for example BPA, the molar ratio of the first dihydroxyaromatic compound to the second dihydroxy aromatic compound is expressedas the sum of the number of moles of resorcinol and hydroquinone useddivided by the number of moles of BPA used. Similarly, where the seconddihydroxy aromatic compound comprises but a single compound, for exampleresorcinol, and the first dihydroxy aromatic compound comprises amixture of compounds, for example, BPA and BPZ(1,1-bis(4-hydroxyphenyl)cyclohexane), the molar ratio of the seconddihydroxy aromatic compound to the first dihydroxy aromatic compound isexpressed as the number of moles of resorcinol used divided by the sumof the number of moles of BPA and BPZ used. As mentioned, in oneembodiment the molar ratio of the second dihydroxy aromatic compound tothe first dihydroxy aromatic compound is in a range between 0.01 and 99.In an alternate embodiment the molar ratio of the second dihydroxyaromatic compound to the first dihydroxy aromatic compound is in a rangebetween 0.05 and 0.7. A copolycarbonate prepared according to the methodof the present invention using resorcinol as the second dihydroxyaromatic compound and BPA as the first dihydroxy aromatic compound inwhich the molar ratio of resorcinol to BPA was 0.7 could contain as muchas 41 mole percent resorcinol derived repeat units if no loss occurredduring the polymerization reaction.

Typically, the method of the present invention is carried out such thatthe amount of diarylcarbonate V employed corresponds to a molar ratio ofdiarylcarbonate V to all dihydroxy aromatic compounds, i.e. the firstand/or second dihydroxy aromatic compounds, initially present in thereaction mixture, the molar ratio being in a range between 0.90 and1.20, preferably between 1.01 and 1.10.

Catalyst Introduction Strategy

The method of the present invention calls for the steps of selecting acatalyst introduction strategy and introducing the catalysts to thereaction mixture in accordance with the selected strategy. As noted thecatalyst introduction strategy incorporates the introduction of anorganic catalyst and an inorganic catalyst.

FIG. 1 shows a melt polymerization processes of the type that may beemployed with the current invention. Precursors of monomer residues (a)and (b), and a carbonate source are introduced to a monomer mix tankwhere they are mixed thereby forming a reaction mixture. The reactionmixture is then sent to a series of process units wherein polymerizationreactions occur and copolymer weight increases. The polymerizationcatalysts are added to the reaction mixture per a selected strategy. Thecatalyst introduction strategies of the present invention includeseveral potential introduction points of organic and/or inorganiccatalysts.

The polymerization catalysts introduction may occur in at least threeschemes. The first scheme is to introduce the polymerization catalyststo the reaction mixture after monomer (a), monomer (b) and the carbonatesource have been melted and prior to substantial polymerization of themonomers. The second strategy is to introduce the polymerizationcatalysts to the reaction mixture or precursors of one or more of themonomer residues prior to melting with the proviso that residence timeof the process from the start of melting until substantialpolymerization has occurred is less than 4 hours. The third strategy isto combine the first two strategies wherein the organic catalyst isintroduced to the reaction mixture prior to melting and the inorganiccatalyst is introduced after melting. The purpose of selecting thestrategy is so that the polymerization catalysts have minimal contactwith the reaction mixture so as to prevent an undesirable oxidationreaction which produces an undesirable color formation within theresulting copolycarbonate.

Strategy 1:

The method of the present invention comprises the strategy ofintroducing the polymerization catalysts to the reaction mixture aftermonomer residues (a), monomer residues (b), and carbonate source aremelted and prior to substantial polymerization. The organic andinorganic catalysts may be introduced to the reaction mixture eithertogether or at separate points.

The introduction of the organic catalyst may occur in a monomer mixtank, or in a feed line to a first process unit. The organic catalystmay be introduced to the reaction mixture as it is prepared if meltingis performed prior to combination of the components, and may beintroduced with the monomer residues or the carbonate source either inthe same feed lines or in a separate feed line.

The introduction of the inorganic catalyst typically occurs at the sametime or after the introduction of the organic catalyst. If theintroduction occurs at the same time, the catalysts may be introducedwithin the same feed or in separate feeds at any of the aforementionedpoints where the organic catalyst may be introduced. It is preferred,however, that the introduction of the catalyst solution to the moltenreaction occur subsequent to the introduction of the precursor ofmonomer residue (a).

If the introduction of the inorganic catalyst occurs a different pointthan the introduction of the organic catalyst then the organic catalystis desirably introduced to the molten reaction mixture prior to a firstprocess unit while the inorganic catalyst is introduced to the moltenreaction mixture at any one of various points prior to substantialpolymerization of the molten reaction mixture. The inorganic catalystmay be introduced in the feed line from the monomer mix tank to a firstprocess unit, or to the molten reaction mixture in the first processunit, or to the molten reaction mixture in a feed line to a secondprocess unit, or to the molten reaction mixture in the second processunit, or to the molten reaction mixture in a feed line to a thirdprocess unit, or to the third process unit itself.

Strategy 2:

The method of the present invention comprises the strategy ofintroducing a polymerization catalyst to the reaction mixture prior tomelting monomer residues (a), monomer residues (b), and carbonate sourcewith the proviso that residence time of the process from the start ofmelting until substantial polymerization has occurred is less than 4hours, more preferably 30 minutes or less, and most preferably 15minutes or less.

The organic and inorganic catalysts may be introduced to the reactionmixture either together or at separate points. The inorganic and organiccatalysts may be introduced to a monomer mix tank or a melter togetherwith monomer residues (a), together with monomer residues (b), togetherwith the carbonate source, in a separate feed or combinations thereof.

Strategy 3:

The method of the present invention comprises the strategy ofintroducing a polymerization catalyst to the reaction mixture whereinthe organic catalyst is introduced to a monomer mix tank or a meltertogether with monomer residue (a), together with monomer residue (b),together with the carbonate source, in a separate feed or combinationsthereof. The inorganic catalyst is then introduced to the moltenreaction mixture, prior to substantial polymerization, within a monomermix tank, a feed line from a monomer mix tank to a first process unit,the first process unit, a feed line to a second process unit, the secondprocess unit, a feed line to a third process unit, the third processunit, or combinations thereof.

An embodiment of the present invention further comprises the step ofintroducing a dihydric phenol or other monomer to the molten reactionmixture within the series of process units through late monomeraddition. This addition of dihydric phenol may occur with in the first,second, third or subsequent process units or the feed lines therebetween.

The method of the present invention may be employed to provide highmolecular weight copolycarbonates. High molecular weightcopolycarbonates are defined as copolycarbonates having a weight averagemolecular weight, M_(w), greater than 15,000 (PS standards). The methodof the present invention may also be employed to provide oligomericcopolycarbonates. Oligomeric copolycarbonates are defined ascopolycarbonates as having weight average molecular weight, M_(w), lessthan 15,000 (PS Standards).

The present invention also provides a method for making a molded articleand a molded article formed from copolycarbonate with improved colorprepared by the method comprising the steps of: preparing a moltenreaction mixture comprising a first dihydroxy aromatic compoundcomprising monomer residue (a), a second dihydroxy aromatic compoundcomprising monomer residue (b), and a carbonate source; selecting acatalyst introduction strategy sufficient to result in a productcopolycarbonate with improved color, wherein the catalyst introductionstrategy is selected from the group consisting of, 1.) introducing apolymerization catalyst to the molten reaction mixture after 0 monomerresidues (a), monomer residues (b), and carbonate source are melted andprior to substantial polymerization, 2.) introducing a polymerizationcatalyst to the reaction mixture or monomer residues prior to meltingwith the proviso that residence time of the process from the start ofmelting until substantial polymerization has occurred is less than 4hours, and 3.) or a combination thereof, wherein the polymerizationcatalyst is an inorganic catalyst, an organic catalyst, or bothinorganic and organic catalyst which may be introduced separately ortogether; introducing the catalyst according to the selected catalystintroduction strategy; introducing the reaction mixture to a series ofprocess units; allowing the reaction mixture to polymerize in the seriesof process units thereby forming copolycarbonate, wherein thecopolycarbonate has improved color as compared to a copolycarbonateformed in a melt process without the steps of selecting a catalystintroduction strategy and introducing catalyst according to the selectedstrategy; and forming a molded article from the copolycarbonate. Themolded articles may be molded by inter alia the processes of injectionmolding, blow molding, extrusion or coextrusion.

Blends of copolymers are typical in industry. Thus the copolycarbonatesprepared using the method of the present invention may be blended withother polymeric materials, for example, other polycarbonates,polyestercarbonates, polyesters and olefin polymers such as ABS.Further, the copolycarbonates prepared using the method of the presentinvention may be blended with conventional additives such as heatstabilizers, mold release agents, and UV stabilizers. These blends maybe molded into various articles such as optical disks, optical lenses,automobile lamp components and the like. Thus, it is an aspect of thepresent invention to provide molded articles comprising the blends ofcopolycarbonate and/or the copolycarbonate produced by the method of thepresent invention.

EXAMPLES

Having described the invention in detail, the following examples areprovided. The examples should not be considered as limiting the scope ofthe invention, but merely as illustrative and representative thereof. Inthe examples, the following measurements were made:

a.) Molecular weight: Mw and Mn were measured by GPC analysis of 1 mg/mlpolymer solutions in methylene chloride versus polystyrene (PS)standards.

b.) Solution Yellowness Index data was measured with a UV/VISspectophotometer on a 10% Copolymer solution in MECl₂. The transmissionwas measured on 3 wavelengths (445 nm, 555 nm, and 600 nm) against aMeCl₂ blank. With the following calculation the solution yellownessindex (sol YI) was calculated;Sol YI=(% T600−% T445)/% T555*100%

c.) Small scale melt polymerization reactions were carried out with BPAand 16 mole % of resorcinol. In this case mole % is defined as 100*(moleco-monomer/(total moles bisphenol). The total amount of DPC (moles)equaled 1.08*(BPA+co-monomer/(total moles bisphenol)). The amount of DPCwas held constant at 25 g in each reaction. As catalysts,TMAH/(BPA+co-monomer)=2.5×10⁻⁴ (mole/mole) andNaOH/(BPA+co-monomer)=1.5×10⁻⁶ (mole/mole) were added as an aqueoussolution (100 μl). Reactions were carried out by mixing bisphenols withDPC.

After nitrogen purging of the reactor system, polymerizations werecarried out according to the following scheme:

TABLE 1 Reaction scheme for small scale melt polymerizations. ReactionStage Time (min) Temp (° C.) P (mbar) 1 480 180 atm 2 60 230 170.0 3 30270  20.0 4 30 300 0.5–1.6

At the end of the reaction, the reactor was brought back to atmosphericpressure with a gentle nitrogen flow, and the polymer was harvested. Themelting time of 480 minutes was chosen to simulate plant conditions.

The results of all the examples below are presented in Table 2 and FIG.2.

Comparative Examples Example 1

In example 1, a batch reactor tube was charged under nitrogen with 19.73g of BPA, 2.38 g of resorcinol, 25.00 g of DPC, and 100 (μl) of anaqueous solution of TMAH and NaOH (2.5×10⁻⁴ and 1.5×10⁻⁶ molescatalyst/mole aromatic dihydroxy compound). Polymerization was carriedout according to steps 1–4 of the scheme in Table 1. The polymer wassampled from the reaction tube.

Example 2

Example 7 was repeated except that the batch reactor tube was chargedunder nitrogen with 24.76 g of BPA, 25.00 g of DPC. After step 1 of thescheme in table 1 100 (μl) of an aqueous solutions of TMAH and NaOH(2.5×10⁻⁴ and 1.5×10⁻⁴ moles catalyst/mole aromatic dihydroxy compound)was added. Polymerization was carried out according to steps 1–4 of thescheme in Table 1. The polymer was sampled from the reaction tube.

Example 3

Example 2 was repeated except that the batch reactor tube was chargedunder nitrogen with 24.76 g of BPA, 25.00 g of DPC. Before step 1 of thescheme in table 1 100 (μl) of an aqueous solutions of TMAH and NaOH(2.5×10⁻⁴ and 1.5×10⁻⁶ moles catalyst/mole aromatic dihydroxy compound)was added. The time of step 1 was 15 minutes. Polymerization was carriedout according to steps 2–4 of the scheme in Table 1. The polymer wassampled from the reaction tube.

Example 4

Example 3 was repeated except that the time of step 1 was 15 minutes.The catalyst was added after step 1 of scheme 1. Polymerization wascarried out according to steps 2–4 of the scheme in Table 1. The polymerwas sampled from the reaction tube.

Example 5

The specification for color of material produced on a commercial scale(OQ1050) at the melt polycarbonate plant. The yellowness index of thecommercial materials is measured on a 1 mm thick sample using a UVspectrophotometer.

Example 6

Example 1 was repeated except that the resorcinol had a differentinitial quality. Polymerization was carried out according to steps 2–4of the scheme in Table 1. The polymer was sampled from the reactiontube.

Invention Examples Example 7

In example 7, a batch reactor tube was charged under nitrogen with 19.73g of BPA 2.38 g of resorcinol, 25.00 g of DPC, after step 1 of thescheme in table 1 100 (μl) of an aqueous solutions of TMAH and NaOH(2.5×10⁻⁴ and 1.5×10⁻⁴ moles catalyst/mole aromatic dihydroxy compound)was added. Polymerization was carried out according to steps 2–4 of thescheme in Table 1. The polymer was sampled from the reaction tube.

Example 8

In example 8, a batch reactor tube was charged under nitrogen with 19.73g of BPA, 2.38 g of resorcinol, 25.00 g of DPC, and 50 (μl) of anaqueous solutions of TMAH and NaOH (2.5×10⁻⁴ and 1.5×10⁻⁶ molescatalyst/mole aromatic dihydroxy compound). After step 1 of the schemein table 1 50 (μl) of an aqueous solutions of TMAH and NaOH (2.5×10⁻⁴and 1.5×10⁻⁶ moles catalyst/mole aromatic dihydroxy compound) was added.Polymerization was carried out according to steps 2–4 of the scheme inTable 1. The polymer was sampled from the reaction tube.

Example 9

Example 1 was repeated except that the time of step 1 was 15 minutes.Polymerization was carried out according to steps 2–4 of the scheme inTable 1. The polymer was sampled from the reaction tube.

Example 10

Example 7 was repeated except that the time of step 1 was 15 minutes.Polymerization was carried out according to steps 2–4 of the scheme inTable 1. The polymer was sampled from the reaction tube.

Example 11

Example 7 was repeated except the catalyst solution was added prior tostep 1 and that the time of step 1 was 2 hours. Polymerization wascarried out according to steps 2–4 of the scheme in Table 1. The polymerwas sampled from the reaction tube.

Example 12

Example 11 was repeated except that the time of step 1 was 4 hours.Polymerization was carried out according to steps 2–4 of the scheme inTable 1. The polymer was sampled from the reaction tube.

Example 13

Example 11 was repeated except that the resorcinol was obtained from adifferent initial quality. Polymerization was carried out according tosteps 2–4 of the scheme in Table 1. The polymer was sampled from thereaction tube.

Example 14

Example 12 was repeated except that the resorcinol was obtained from adifferent initial quality. Polymerization was carried out according tosteps 2–4 of the scheme in Table 1. The polymer was sampled from thereaction tube.

TABLE 2 Properties of the polymers of which the preparation is describedin the examples above. Example # Summary YI Comparative  1 BPA/Res-PC, 8hr melting, cat before melting 8.31  2 BPA-PC cat. Added after melting1.16  3 BPA-PC 15 minutes melting time, cat before 0.44 melting  4BPA-PC 15 minutes melting time, cat after melting 0.66  5 CommercialBPA-PC 1.20  6 BPA/Res-PC, 8 hr melting, cat before melting 11.10Invention  7 BPA/Res-PC Cat added after melting 1.00  8 BPA/Res-PC TMAHbefore/NaOH after melting 2.08  9 BPA/Res-PC 15 minutes melt, cat beforemelting 1.42 10 BPA/Res-PC 15 minutes melt, cat after melting 0.92 11BPA/Res-PC 2 hr melting time, cat before melting 1.60 12 BPA/Res-PC 4 hrmelting time, cat before melting 1.50 13 BPA/Res-PC 2 hr melting time,cat before melting 2.00 14 BPA/Res-PC 4 hr melting time, cat beforemelting 2.70

1. A method of producing a copolycarbonate with improved color whereinthe method comprises the steps of, i. preparing a molten reactionmixture comprising a first dihydroxy aromatic compound comprisingmonomer residue (a), a second dihydroxy aromatic compound comprisingmonomer residue (b), and a carbonate source, wherein monomer residue (a)is a quinone structure, or a structure capable of forming a quinonestructure upon oxidation, wherein monomer residue (b) is a quinonestructure, or a structure capable of forming a quinone structure uponoxidation different from monomer residue (a) or is,

 where B is

 —O—, —CO—, —S—, —SO₂—, a C₆–C₂₀ aromatic radical, or a C₆–C₂₀cycloaliphatic radical; the groups R¹ and R² are independently ahydrogen atom, C₁–C₂₀ alkyl radical, C₄–C₂₀ cycloalkyl radical, orC₄–C₂₀ aryl radical; or R¹ and R² together form a C₄–C₂₀ cycloaliphaticring which is optionally substituted by one or more C₁–C₂₀ alkyl C₆–C₂₀aryl, C₅–C₂₁ aralkyl, C₅–C₂₀ cycloalkyl groups or a combination thereof,R³ is a divalent hydrocarbylene group, and R⁴ and R⁵ are independently ahydrogen atom, halogen atom, nitro group, cyano group, C₁–C₂₀ alkylradical C₄–C₂₀ cycloalkyl radical, or C₆–C₂₀ aryl radical and p and qare both integers from 0 to 4, ii. selecting a catalyst introductionstrategy sufficient to result in a product copolycarbonate with improvedcolor, wherein the catalyst introduction strategy is selected from thegroup consisting of,
 1. introducing a polymerization catalyst to themolten reaction mixture after monomer residues (a), monomer residues(b), and carbonate source are melted and prior to substantialpolymerization,
 2. introducing a polymerization catalyst to the reactionmixture or monomer residues prior to melting with the proviso thatresidence time of the process from the start of melting untilsubstantial polymerization has occurred is less than 4 hours, and
 3. ora combination thereof, wherein the polymerization catalyst is aninorganic catalyst, an organic catalyst, or both inorganic and organiccatalyst which may be introduced separately or together, iii.introducing the catalyst according to the selected catalyst introductionstrategy, iv. introducing the reaction mixture to a series of processunits, and v. allowing the reaction mixture to polymerize in the seriesof process units thereby forming copolycarbonate, wherein thecopolycarbonate has improved color as compared to a copolycarbonateformed in a melt process without the steps of selecting a catalystintroduction strategy and introducing catalyst according to the selectedstrategy.
 2. The method of claim 1, wherein the polymerization catalystcomprises an organic and inorganic catalysts and is introduced to thereaction mixture after monomer residues (a), monomer residues (b), andcarbonate source are melted and prior to substantial polymerization. 3.The method of claim 2, wherein the inorganic catalyst is NaOH and theorganic catalyst is selected from the group consisting of TMAH, TBPA,and combinations thereof.
 4. The method of claim 2, wherein monomerresidue (a) has the structure,

where each R¹⁰ is independently at each occurrence a hydrogen atom,halogen atom, nitro group, cyano group, C₁–C₂₀ alkyl, C₄–C₂₀ cycloalkylradical, C₄–C₂₀ aryl radical, and n is an integer from 0 to
 4. 5. Themethod of claim 4, wherein monomer residue (a) is catechol, resorcinol,hydroquinone, butyl hydroquinone, methyl hydroquinone or any combinationthereof.
 6. The method of claim 2, wherein monomer residue (b) is BPA.7. The method of claim 2, wherein the carbonate source is diphenylcarbonate.
 8. The method of claim 2, wherein the carbonate source is anactivated carbonate.
 9. The method of claim 8, wherein the activatedcarbonate is bismethylsalicylcarbonate.
 10. The method of claim 2,wherein up to 50 mole % of the carbonate source is selected from thegroup consisting of dicarboxylic acids, dicarboxylic acid esters,dicarboxylic acid halide or any combination thereof.
 11. The method ofclaim 2, wherein the inorganic and organic catalysts are introducedtogether.
 12. The method of claim 11, wherein the inorganic and organiccatalysts are introduced with monomer residue (a), monomer residue (b),the carbonate source or combinations thereof.
 13. The method of claim11, wherein the inorganic and organic catalysts are introduced to thereaction mixture in a separate feed to a monomer mix tank, a firstprocess unit, or a feed line to a first process unit.
 14. The method ofclaim 2, wherein the inorganic and organic catalysts are introduced tothe molten reaction mixture at separate points.
 15. The method of claim14, wherein the organic catalyst is introduced to the molten reactionmixture prior to a first process unit and the inorganic catalyst isintroduced to the molten reaction mixture after the introduction of theorganic catalyst and prior to substantial polymerization of the reactionmixture.
 16. The method of claim 14, wherein the organic catalyst isintroduced with monomer residue (a), monomer residue (b), the carbonatesource or combinations thereof and the inorganic catalyst is introducedto the molten reaction mixture after the introduction of monomer (a).17. The method of claim 14, wherein the inorganic catalyst is introducedto the molten reaction mixture in a feed line from a monomer mix tank toa first process unit, the first process unit, a feed line to a secondprocess unit, the second process unit, a feed line to a third processunit, the third process unit, or combinations thereof.
 18. The method ofclaim 2, wherein the method further comprises the step of introducing adihydric phenol to the molten reaction mixture within the series ofprocess units through late monomer addition.
 19. The method of claim 1,wherein the polymerization catalyst comprises organic and inorganiccatalysts and is introduced to the reaction mixture or monomer residuesprior to melting with the proviso that residence time of the processfrom the start of melting until substantial polymerization has occurredis less than 4 hours.
 20. The method of claim 19, wherein the residencetime of the process from the start of melting until substantialpolymerization has occurred is 30 minutes or less.
 21. The method ofclaim 20, wherein the residence time of the process from the start ofmelting until substantial polymerization has occurred is 15 minutes orless minutes.
 22. The method of claim 19, wherein the inorganic catalystis NaOH and the organic catalyst is selected from the group consistingof TMAH, TBPA, and combinations thereof.
 23. The method of claim 19,wherein monomer residue (a) has the structure,

where each R¹⁰ is independently at each occurrence a hydrogen atom,halogen atom, nitro group, cyano group, C₁–C₂₀ alkyl, C₄–C₂₀ cycloalkylradical, C₄–C₂₀ aryl radical, and n is an integer from 0 to
 4. 24. Themethod of claim 19, wherein monomer residue (a) is catechol, resorcinol,hydroquinone, butyl hydroquinone, methyl hydroquinone or any combinationthereof.
 25. The method of claim 19, wherein monomer residue (b) is BPA.26. The method of claim 19, wherein the carbonate source is diphenylcarbonate.
 27. The method of claim 19, wherein the carbonate source isan activated carbonate and is bismethylsalicylcarbonate.
 28. The methodof claim 19, wherein up to 50 mole % of the precursor of the carbonatesource is derived from the group consisting of dicarboxylic acids,dicarboxylic acid esters, dicarboxylic acid halide or any combinationthereof.
 29. The method of claim 19, wherein the inorganic and organiccatalysts are introduced together or separately.
 30. The method of claim19, wherein the inorganic and organic catalysts are introduced to amonomer mix tank or a melter together with monomer residue (a), togetherwith monomer residue (b), together with the carbonate source, in aseparate feed or combinations thereof.
 31. The method of claim 1,wherein the polymerization catalyst comprises organic and inorganiccatalysts, wherein the organic catalyst is introduced to the reactionmixture or monomer residues prior to melting with the proviso thatresidence time of the process from the start of melting untilsubstantial polymerization has occurred is less than 4 hours, andwherein the inorganic catalyst is introduced to the reaction mixtureafter monomer residues (a), monomer residues (b), and carbonate sourceare melted, and wherein the introduction occurs prior to substantialpolymerization.
 32. The method of claim 31, wherein the residence timeof the process from the start of melting until substantialpolymerization has occurred is 30 minutes or less.
 33. The method ofclaim 32, wherein the residence time of the process from the start ofmelting until substantial polymerization has occurred is 15 minutes orless.
 34. The method of claim 31, wherein the inorganic catalyst is NaOHand the organic catalyst is selected from the group consisting of TMAH,TBPA, and combinations thereof.
 35. The method of claim 31, whereinmonomer residue (a) has the structure,

where each R¹⁰ is independently at each occurrence a hydrogen atom,halogen atom, nitro group, cyano group, C₁–C₂₀ alkyl, C₄–C₂₀ cycloalkylradical, C₄–C₂₀ aryl radical, and n is an integer from 0 to
 4. 36. Themethod of claim 35, wherein monomer residue (a) is catechol, resorcinol,hydroquinone, butyl hydroquinone, methyl hydroquinone or any combinationthereof.
 37. The method of claim 31, wherein monomer residue (b) is BPA.38. The method of claim 31, wherein the carbonate source is diphenylcarbonate.
 39. The method of claim 31, wherein the carbonate source isan activated carbonate and is bismethylsalicylcarbonate.
 40. The methodof claim 31, wherein up to 50 mole % of the precursor of the carbonatesource is derived from the group consisting of dicarboxylic acids,dicarboxylic acid esters, dicarboxylic acid halide or any combinationthereof.
 41. The method of claim 31, wherein the organic catalyst isintroduced to a monomer mix tank or a melter together with monomerresidue (a), together with monomer residue (b), together with thecarbonate source, in a separate feed or combinations thereof, andwherein the inorganic catalyst is introduced to the molten reactionmixture, within a monomer mix tank, a feed line from a monomer mix tankto a first process unit, the first process unit, a feed line to a secondprocess unit, the second process unit, a feed line to a third processunit, the third process unit, or combinations thereof.
 42. The method ofclaim 1, wherein the copolymer has a molecular weight Mw of at least10,000 g/mole (Polystyrene standards) and the molecular weight Mw issubsequently increased to a value higher than 25,000 g/mole (Polystyrenestandards) using a standard extrusion step.
 43. The method of claim 1,wherein the copolymer has a molecular weight Mw of at least 10,000g/mole (Polystyrene standards) and the molecular weight Mw issubsequently increased to a value higher than 25,000 g/mole (Polystyrenestandards) by further reaction of oligomers by means of solid statepolymerization.
 44. A molded article formed from copolycarbonate withimproved color prepared by the method comprising the steps of, i.preparing a molten reaction mixture comprising a first dihydroxyaromatic compound comprising monomer residue (a), a second dihydroxyaromatic compound comprising monomer residue (b), and a carbonatesource, wherein monomer residue (a) is a quinone structure, or astructure capable of forming a quinone structure upon oxidation, whereinmonomer residue (b) is a quinone structure, or a structure capable offorming a quinone structure upon oxidation different from monomerresidue (a) or is,

 where B is

 —O—, —CO—, —S—, —SO₂—, a C₆–C₂₀ aromatic radical, or a C₆–C₂₀cycloaliphatic radical; the groups R¹ and R² are independently ahydrogen atom, C₁–C₂₀ alkyl radical, C₄–C₂₀ cycloalkyl radical, orC₄–C₂₀ aryl radical; or R¹ and R² together form a C₄–C₂₀ cycloaliphaticring which is optionally substituted by one or more C₁–C₂₀ alkyl, C₆–C₂₀aryl, C₅–C₂₁ aralkyl, C₅–C₂₀ cycloalkyl groups or a combination thereof,R³ is a divalent hydrocarbylene group, and R⁴ and R⁵ are independently ahydrogen atom, halogen atom, nitro group, cyano group, C₁–C₂₀ alkylradical C₄–C₂₀ cycloalkyl radical, or C₆–C₂₀ aryl radical and p and qare both integers from 0 to 4, ii. selecting a catalyst introductionstrategy sufficient to result in a product copolycarbonate with improvedcolor, wherein the catalyst introduction strategy is selected from thegroup consisting of,
 1. introducing a polymerization catalyst to themolten reaction mixture after monomer residues (a), monomer residues(b), and carbonate source are melted and prior to substantialpolymerization,
 2. introducing a polymerization catalyst to the reactionmixture or monomer residues prior to melting with the proviso thatresidence time of the process from the start of melting untilsubstantial polymerization has occurred is less than 4 hours, and
 3. ora combination thereof, wherein the polymerization catalyst is aninorganic catalyst, an organic catalyst, or both inorganic and organiccatalyst which may be introduced separately or together, iii.introducing the catalyst according to the selected catalyst introductionstrategy, iv. introducing the reaction mixture to a series of processunits, v. allowing the reaction mixture to polymerize in the series ofprocess units thereby forming copolycarbonate, wherein thecopolycarbonate has improved color as compared to a copolycarbonateformed in a melt process without the steps of selecting a catalystintroduction strategy and introducing catalyst according to the selectedstrategy, and vi. forming a molded article from the copolycarbonate. 45.A method for making a molded article formed from copolycarbonate withimproved color prepared by the method comprising the steps of, i.preparing a molten reaction mixture comprising a first dihydroxyaromatic compound comprising monomer residue (a), a second dihydroxyaromatic compound comprising monomer residue (b), and a carbonatesource, wherein monomer residue (a) is a quinone structure, or astructure capable of forming a quinone structure upon oxidation, whereinmonomer residue (b) is a quinone structure, or a structure capable offorming a quinone structure upon oxidation different from monomerresidue (a) or is,

 where B is

 —O—, —CO—, —S—, —SO₂—, a C₆–C₂₀ aromatic radical, or a C₆–C₂₀cycloaliphatic radical; the groups R¹ and R² are independently ahydrogen atom, C₁–C₂₀ alkyl radical, C₄–C₂₀ cycloalkyl radical, orC₄–C₂₀ aryl radical; or R¹ and R² together form a C₄–C₂₀ cycloaliphaticring which is optionally substituted by one or more C₁–C₂₀ alkyl, C₆–C₂₀aryl, C₅–C₂₁ aralkyl, C₅–C₂₀ cycloalkyl groups or a combination thereof,R³ is a divalent hydrocarbylene group, and R⁴ and R⁵ are independently ahydrogen atom, halogen atom, nitro group, cyano group, C₁–C₂₀ alkylradical C₄–C₂₀ cycloalkyl radical, or C₆–C₂₀ aryl radical and p and qare both integers from 0 to 4, ii. selecting a catalyst introductionstrategy sufficient to result in a product copolycarbonate with improvedcolor, wherein the catalyst introduction strategy is selected from thegroup consisting of,
 1. introducing a polymerization catalyst to themolten reaction mixture after monomer residues (a), monomer residues(b), and carbonate source are melted and prior to substantialpolymerization,
 2. introducing a polymerization catalyst to the reactionmixture or monomer residues prior to melting with the proviso thatresidence time of the process from the start of melting untilsubstantial polymerization has occurred is less than 4 hours, and
 3. ora combination thereof, wherein the polymerization catalyst is aninorganic catalyst, an organic catalyst, or both inorganic and organiccatalyst which may be introduced separately or together, iii.introducing the catalyst according to the selected catalyst introductionstrategy, iv. introducing the reaction mixture to a series of processunits, v. allowing the reaction mixture to polymerize in the series ofprocess units thereby forming copolycarbonate, wherein thecopolycarbonate has improved color as compared to a copolycarbonateformed in a melt process without the steps of selecting a catalystintroduction strategy and introducing catalyst according to the selectedstrategy, and vi. forming a molded article from the copolycarbonate.